Closure elements for pharmaceutical purposes such as stoppers or plugs are often subjected to a treatment which involves firstly washing them in a washing phase by means of high-purity, germ-free water. The washing operation can be effected with or without the addition of one or more detergents. To initiate the washing phase a process container is firstly filled with the closure elements or plugs and then water is added. For the actual washing operation, the closure elements are moved by means of compressed air which is supplied to the process container. The washing water is then drained away again, after the treatment operation. The washing phase and the drainage phase may then be followed by a silicone-coating operation, in a third phase. For that purpose, hot, highly pure water is again supplied to the container, with the water being mixed with a metered amount of silicone. The water is then removed and in a subsequent further phase sterilisation is effected using steam.
After the steam sterilisation procedure, the closure elements are still wet and have to be dried before being removed from the process container. In order that few or no drops remain on the closure elements or plugs, the closure elements or plugs may be moved around in the process container in such a way that they are dried to the greatest reasonable possible extent.
To do that, the process container may be moved mechanically during the feed of hot air into same, in order thereby to provide that during the drying operation the closure elements respectively adopt different positions from their previous positions in the process container, so that the hot air can also reach those parts and regions of the closure elements which, when they were in their previous position, either bore against the inside wall surface of the process container or against other closure elements or plugs. A disadvantage in that respect is that complicated and costly equipment is required to produce the above-mentioned mechanical movement of the process container. In addition, the fact that the closure elements are continuously rubbing against each other in the drying procedure means that undesirable abrasion and erosion thereof occurs. Furthermore, particularly when dealing with silicone-coated closure elements, the drying procedure may often fall foul of the undesirable phenomenon that the closure elements or plugs stick together and thus form clumps, resulting in what can be called compacting of the closure elements within the process container.
Drying procedures can also be implemented in fluidised bed driers, in which respect attention may be directed for example to K Kroll: Trockner und Trocknungsverfahren, [`Driers and drying processes`], Springer-Verlag 1959, pages 275 ff. In such a drier air flows constantly upwardly through a layer of particles at such a rate that the particles are slightly lifted and loosened up but are not carried away by the air flow. In such a procedure all the parts of the material are continuously in movement. Such an apparatus and procedure can thus be used to dry materials which are capable of a trickle flow, which also includes plastic materials. A disadvantage in this respect however is also the fact that the movement of the particles means that they are frequently striking and knocking against each other and thus suffer from a considerable degree of abrasion and erosion. Furthermore a fluidised bed drier of that kind is not suitable for particles which have a tendency to compacting as discussed above.
DE 42 11 485 C2 describes a process for removing moisture from the interior of a solid material, for example wood. In that procedure, the wood is firstly acted upon by a high pressure which mechanically drives the moisture out of the solid material, and it is then exposed to a periodically rapidly changing pressure in order to remove the residual moisture. This operating procedure also involves the risk of severe particle abrasion and erosion, due to the continual fluctuations in pressure.